Huh. Looking at the pin #defines in my C code, I did use the LB4, the latch value, for SDO. Now I've never been sure I fully understood the difference. I have an output value now.
I stripped the last 6 bits of channel & parity, and get these values:
Applying 5V gives 0xc00000. It's a totally static value with no noise. Since bit 23 is a sign bit indicating 'positive', it's 0x40000, or 262144.
Grounding the input gave 0x801AD1, the exact value changes every sample. Stripping the sign bit gives 0x001ad1, or 6865.
So the value from giving gnd is small and looks like it'd be zero if not for ground noise. But why is the value when applying 5V so far from the 0x7fffff I'd expect??? And why is it reading a totally static value? There should logically be some noise in it.